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Threatened species

Climate change making polar bears go hungry, study shows

An increasing number of polar bears can't catch enough prey to fill their stomach, researchers found. As a result, many bears are losing weight — a development that could push the species closer to extinction.

Imagine you have to walk through ice and snow all day for most of the year. You'd work up quite an appetite — and get hungrier the more distance you'd cover.

That sums up the life of a polar bear.

Living in the icy Arctic, they prey on fat-rich mammals like ringed seals to sustain themselves in this harsh environment.

The iconic animals require 1.6 times more energy than was estimated in the 1990s, researchers at the US Geological Survey, the Alaska Science Center in Anchorage, and at the University of California at Santa Cruz report in the journal "Science."

"They need to be catching a lot of seals," Anthony Pagano, a PhD candidate at UC Santa Cruz said.

Less sea ice makes them wander more

In total, the bears would have to eat one adult ringed seal or 19 newborn seal pups every 10 to 12 days to avoid starvation, the researchers say.

They assume the bears' hunger for food is greater than previously estimated due to a lack of sea ice; that makes the bears have to roam over greater distances to find and kill prey.

According to a study by the University of Colorado, the extent of sea ice across the Arctic is decreasing at a rate of 14 percent per decade.

Polar bears need sea ice to hunt seals — but that ice is shriking

The problem is that many polar bears can't seem to find enough food to satisfy their high energy requirements.

Five of the nine bears that were examined in the study lost weight, amounting to approximately 10 percent of their body mass during the eight- to 11-day period.

"Increases in movement [...] mediated by the loss of sea ice habitat are likely to have negative [...] effects on polar bear reproductive success, and ultimately, their populations," the researchers conclude.

Polar bears in a warming world

The fact that climate change might hit polar bears hard is not a surprise.

But certainly, vanishing sea ice makes the predators' hunt for seals more difficult.

It was once thought that polar bears could go into a kind of walking hibernating state when no food is around, decreasing their metabolic rates and thus their energy requirements. This assumption was found not to be true.

"Two-thirds of the world's polar bears could die out by 2050," cautions WWF, demanding an immediate decline in greenhouse gas emissions so that the bears can stand a chance of survival.

Conservationists warn that polar bears might go extinct soon

According to the International Union for Conservation of Nature, there are approximately 26,000 polar bears left. The species is categorized as "vulnerable." In the US, it's considered a threatened species.

IUCN experts estimate that the population could decrease by 30 to 50 percent if the loss of sea ice continues.

Observing bears' hunting successes close up

How did Pagano and his colleagues prove that it's harder for polar bears to find food in a world with less sea ice?

The researchers went there and observed the bears.

"We've been documenting declines in polar bear survival rates, body condition, and population numbers over the past decade," Pagano said. "This study identifies the mechanisms that are driving those declines by looking at the actual energy needs of polar bears and how often they're able to catch seals."

They collared nine adult female polar bears on the sea ice of the Beaufort Sea in Alaska with a GPS video camera and observed the bears for discreet time periods over three consecutive years.

The GPS told them the distances the bears wandered, and the video camera recorded if the bears were successful in killing and eating prey.

A collar with GPS and video camera told the researchers when and where the bears hunted

To measure the animals' energy needs, the researchers injected them with a tracable (nonradioactive) element.

By comparing the bears' blood samples before and after, they could calculate the amount of carbon dioxide that the animal had produced, and thus its metabolic rate.

"An increasing proportion of bears are unable to meet their energy demands," the authors concluded.

Still hope

While the recent study might be bad news, it doesn't automatically mean the end for polar bears, comments Jörns Fickel, a evolution geneticist at the Leibniz institute for Zoo and Wildlife Research in Berlin.

"Nobody can conclude from the study that polar bears will get extinct," he tells DW. "I am still optimistic that the species will make it."

Will the species survive climate change?

From an evolutionary point of view, a loss in body weight in some animals doesn't necessarily mean that the total number of polar bears will decline, Fickel stresses.

"In a population, there are always individuals who cope better or worse with any changes."

Fickel points out that the species has seen many warmer periods during their existence, and that they might be able to adjust to a warmer world – as long as there is a healthy seal population, that is.

But still, "when I see pictures of big glacial blocks breaking away and the sea ice is retreating, I get worried," Fickel admits.

As a scientist, he stresses that we shouldn't go off of gut feelings, but rather reliable data — "and for polar bears, those [data] aren't there yet."

So don't give up yet on the powerful polar bear.

Bears in peril

The bears

Bears: They can walk upright, see in color — unlike most other mammals — and most are ominivores like us. Yes, we are distantly related to bears — bears and humans share a common, rat-like ancestor from about 100 million years ago. The American black bear, pictured here, ranges across North America and is an excellent tree climber. Black bears can also be cinnamon or even platinum in color.

Bears in peril

Brown bear

Brown bears, or Ursus arctos, are the most widely distributed bear in the world, ranging across Eurasia and North America. These bears tend to be solitary, but sometimes congregate to feast on fish. Ahead of hibernation, brown bears gorge themselves on fat to prepare for winter. Brown bears living inland in the lower 48 US states are known as grizzly bears — an iconic symbol of wilderness.

Bears in peril

Awoken early

Although brown bears have been hunted to extinction in portions of their native habitat, they continue to survive in Europe in isolated pockets. Above, a mother bear watches over her cub as it struggles through thick snow in Finland. Bears' summer feasting creates a thick layer of fat they survive off in winter, typically in hibernation. But changing weather is also altering hibernation patterns.

Bears in peril

Lend a hand

In addition to being able to walk upright, brown bears can also run very quickly on all fours — up to 30 miles per hour (64 kph). This helps them hunt down other animals to eat. The anatomy of bear paws is so remarkably similar to that of human hands and feet that skeletal remains, and footprints, are often mixed up. Above, a brown bear gets a tooth operation in Germany.

Bears in peril

Andean bear

South America even gets its "own" bear: the spectacled or Andean bear. Per its name, the species often sports light-colored fur around its eyes. The IUCN classifies this species as "vulnerable" — the bear has lost its wooded habitat on the slopes of the Andes due largely to forest-clearing for crops and cattle farming.

Bears in peril

The sun ...

Sun bears, or Malayan sun bears, have a bib-shaped golden patch on their chests, which for some cultures represents the rising sun. Indeed, the sun bear lives in the Far East, making its home in tropical forests of southern Asia. The IUCN classifies sun bears as "vulnerable" — it's among the rarest bear species, and is under threat due to habitat loss, the pet trade and hunting for "medicine."

Bears in peril

... and the moon

Moon bears, also known as Asiatic black bears, are likewise threatened due largely to poaching. Demand for bile from the gall bladders of black bears is driving widespread hunting, capture, captivity and trade — moon bears are even kept on mostly illegal "bile farms." Although there is no scientifically proven human health benefit from consuming bear bile, the trade continues.

Bears in peril

Sloth bear

The sloth bear is also "vulnerable," as its lowland forest in the Indian subcontinent disappears. Sloth bears survive on insects and have particularly shaggy fur — they are also targets for poaching and the pet trade. Pictured above, "Buddu" the sloth bear was adopted by a family in India after wandering into the village after a herd of goats. Wildlife officials later rescued the bear.

Bears in peril

Little giants

We all know and love pandas — panda cubs are particularly cute. Giant pandas were upgraded from "endangered" to "vulnerable" in 2016 due to vigorous efforts by the Chinese government to preserve the iconic animal. Such efforts include a captive breeding program, which achieved record success in 2017 with 42 pandas born.

Bears in peril

Beloved bear

Like many other bears, pandas are threatened above all from loss of habitat. Infrastructure projects in particular are cutting into what's left of the cool, humid bamboo forest high in the mountains of western China where pandas make their home. Since bamboo is so nutritionally poor, the bears have to eat up to 84 pounds (38 kilograms) per day — giant pandas spend much of their waking time eating.

Bears in peril

Polar bear

Last but not least ... another icon. Technically classified as a marine mammal, polar bears are carnivorous. For hunting seals and other ocean animals, polar bears rely on sea ice, which is declining as the Arctic melts due to climate change. The plight of the polar bear has become synonymous with the fight against global warming. As the planet heats up, time is running out for these bears.